1. Department of Clinical Sciences, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, PO box 7054, 75007 Uppsala, Sweden.
2. Ekeskogs Riding Academy, Ekeskogs 906, 62375 Klintehamn, Sweden.
3. Department of Anatomy, Physiology and Biochemistry, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, PO box 7054, 75007 Uppsala, Sweden.